X-10 has been around the longest, and is by far the least expensive. X-10 was originally designed to send its signals through existing power wiring, but was later adapted to transmit wirelessly as well. X-10 has a broad catalog of available devices, but its primary downfall is its lack of robustness. The problem is that the protocol is specified with one-way communication and includes no checks for commands making it through to the targeted device.

UPB was designed to counter X-10’s weaknesses by utilizing a higher voltage and stronger signal. UPB is a powerline-only communication protocol, so some devices are much harder to install. In addition, a high cost for the technology has made UPB prohibitive to buy into, and has likely stunted the growth of the technology.

Z-wave is a newer protocol and is dependent on wireless signals at 908.42MHz (though that varies slightly depending on the country in which the device is intended for sale). Due to its wireless nature, it has become very popular for refitting older homes with home automation, and since it operates at ~900MHz there is no need to worry about wireless network interference. Some of the concerns of Z-wave are its proprietary technology, radio congestion with larger deployments, and low tolerance for failed, moved, or removed devices.

Insteon is another newer protocol, and it utilizes both powerline and 915MHz wireless signals for a robust network. Each device acts a transceiver in that it will receive a signal and transmit the signal again if it is not the addressed device. Insteon can also communicate via X-10 signals, an ability that has made it popular for those who have already invested in X-10 and want to update to a newer, more robust protocol.

xAP is an open protocol used for home automation and supports integration of telemetry and control devices primarily within the home. Common communications networks include RS232, RS485, Ethernet& wireless. xAP protocol always uses broadcast for sending the messages. All the receivers listens to the message and introspects the message header to verify whether the message is of its interest. xAP protocol has the following key advantages.

It makes use of existing infrastructure wherever possible (for example it can co-exist with various physical layers like RS232 or wireless LAN)

It can even intercommunicate between multiple networks like RS232 or wireless by just deploying a physical bridge.

xAP does not require any central controller. All nodes can act as sender or receiver.

xAP system provides distributed and fault tolerant architecture which allows continuous operation of systems even in the event of component failures.

xPL is an open protocol intended to permit the control and monitoring of home automation devices. The primary design goal of xPL is to provide a rich set of features and functionality, whilst maintaining an elegant, uncomplicated message structure. The protocol includes complete discovery and auto-configuration capabilities which support a fully “plug-n-play” architecture – essential to ensure a good end-user experience.

xPL benefits from a strongly specified message structure, required to ensure that xPL-enabled devices from different vendors are able to communicate without the risk of incompatibilities.

Communications between xPL applications on a Local Area Network (LAN) use UDP on port 3865.

xPL development has primarily occurred in the DIY community, where users have written connecting software to existing protocols and devices. Some examples include bridges to other home automation protocols like Z-Wave and UPB Commercially, the Logitech SqueezeCenter software for the Squeezebox supports xPL.